Over 50,000 people die each year because of congestive heart failure, a condition that often cannot be treated with drug or surgical therapies. Moreover, nearly 550,000 new patients are diagnosed with congestive heart failure each year. For most patients that suffer heart failure, the only option is heart transplantation via an organ donor or by artificial means. The scarcity of suitable donor hearts has left patients and doctors with no choice but to look to artificial heart therapies. Fortunately, great strides have been made in the development of ventricular assist devices (VADs). Instead of totally replacing heart function, a VAD augments the existing heart's ability to pump blood. These devices have saved many patients who would not have survived without a heart transplant. Despite it success, current VAD technology still has much room for improvement. The development of a viable long term total artificial heart replacement still remains the ultimate goal.
In the past, total artificial hearts (TAHs) have been based on a pulsatile system in an effort to mimic the human heart. However, such devices require prosthetic valves and external vent tubes. The prosthetic valves in pulsatile systems are prone to causing blood damage and blood clots while external vent tubes are a likely source for infection. Furthermore, current TAHs are still large, expensive to produce, and not anatomically suitable for implantation in small adults and children. In recent years, research has focused on continuous flow systems as an alternative to the traditional pulsatile model. In a continuous flow system, blood is continuously pumped through the body rather than pulsing the blood rhythmically as in the human heart.
Continuous flow systems offer several advantages over pulsatile systems. First, continuous flow pumps are generally smaller than pulsatile pumps. Shrinking the size of artificial heart devices will allow doctors to treat women and small children who previously were not candidates for pulsatile TAHs. Second, continuous flow pumps consume less energy than pulsatile systems. This property is important for quality of life issues, allowing the device to run on smaller batteries. Finally, continuous flow pumps have been developed that are magnetically driven with no mechanical bearings or valves, dramatically decreasing any chance of blood damage or long term failure.
Unfortunately, continuous flow pumps are not without drawbacks. The main problem with continuous flow pumps is their inability to auto-regulate or balance flow and pressure across the left and right side of the heart. Even in a healthy human heart, there is a 10 to 15 percent difference in flow and pressure between the left and right sides of the heart. This difference is because of the greater resistance in the systemic circulation i.e. the left side of the heart. In biventricular assist devices, where the patient's natural atria are utilized, an inability to auto-regulate flow and pressure may result in atrial collapse, a potentially fatal condition.
Prior attempts at overcoming this problem have utilized electronic monitoring and control for changing the pump speed. However, any solution involving electronic control systems will likely be unsuitable for long term patient survival due to the inherent limitations on the reliability and longevity of electronic sensors and control systems. Therefore, the ideal continuous flow system would contain a means to auto-regulate without the need for electronic control systems.
Consequently, there is a need for a simple system to auto-regulate flow and pressure balance in TAHs employing continuous flow pumps that may be used to temporarily or permanently replace a defective human heart.